Electrical connections for metal electrodes

ABSTRACT

THE JOINING IN ELECTRICAL CONNECTION UNDER CORROSIVE CONDITIONS OF A PART MADE OF TITANIUM AND A PART MADE OF STEEL BY THE USE OF ENGAGING THREADS OR LUGS IS DIFFICULT. HOWEVER IF EACH PART IS FIRST COATED WITH A LAYER OF SOFTER BUT COMPATIBLE NON-OXIDIZING METAL, THEN THE TWO PARTS CAN BE JOINED TOGETHER IN A TIGHT ELECTRICAL/MECHANICAL JOINT. A TYPICAL SYSTEM IS A PLATINUM COATING FOR TITANIUM AND EITHER SILVER OR NICKEL UNDER COPPER FOR STEEL.

1974 c. w. STEPHENSON Ill, EITAL 3, 8

ELECTRICAL CONNECTIONS FOR METAL ELECTRODES Filed June '1 1972 UnitedStates Patent Office 3,788,966 Patented Jan. 29, 1974 3,788,966ELECTRICAL CONNECTIONS FOR METAL ELECTRODES Orlando W. Stephenson III,Ann Arbor, and John E.

Schmidt, Southgate, Mich., assignors to BASF Wyandotte Corporation,Wyandotte, Mich.

Filed June 7, 1972, Ser. No. 260,394 Int. Cl. B01k 3/10 US. Cl. 204-2566 Claims ABSTRACT OF THE DISCLOSURE The joining in electrical connectionunder corrosive conditions of a part made of titanium and a part made ofsteel by the use of engaging threads or lugs is difficult. However ifeach part is first coated with a layer of softer but compatiblenon-oxidizing metal, then the two parts can be joined together in atight electrical/mechanical joint. A typical system is a platinumcoating for titanium and either silver or nickel under copper for steel.

BACKGROUND (1) Field of the invention This invention relates toelectrolytic cells having both a metal anode and a metal cathode andparticularly to electrolytic cells for the production of chlorine andcaustic. A new method of making electrical and mechanical connectionbetween the metal cathode and metal anode is provided.

(2) Description of the prior art Typically the electrolytic cell used inthe production of chlorine and caustic from an aqueous alkali metalchloride solution has been a diaphragm cell with a graphite anode. Morerecently dimensionally stable metal anodes of a practical nature havebeen developed for use in the diaphragm cell. These metal anodes haveadditionally made it possible to consider the filter press constructionfor the diaphragm cell. However, to develop a practical filter presscell, internal electrical connections are necessary in order to obtain acompact unit. It is readily recognized that the internal conditions ofthese cells is very corrosive to many metals thereby requiring strongelectrical/mechanical connections which can be easily protected.

SUMMARY OF THE INVENTION In accordance with this invention there isprovided in a bipolar electrolytic filter press cell for the productionof chlorine from an aqueous alkali metal chloride solution wherein theanode is made of a valve metal and the cathode is made of a ferrousmetal said anode and said cathode being in electrical connection bybolting one to another, the improvement which comprises insertingthrough one of the foregoing electrodes a bolt having thread engagingmeans and made of substantially the same metal as the electrode, theother electrode having female thread engaging means said ferrous metalthreads being coated with a coinage metal plating and said valve metalthreads being plated with at least one platinum group metal whereby whenthe electrical connnection is made the softer platinum group metal andthe coinage metal are driven into solid contact with each other therebymaking a solid electrical connection and a strong mechanical connectionunder shearing stress.

DESCRIPTION OF THE DRAWING The drawing is a cutaway view along thelength of the engaging bolt showing a ferrous metal cathode and valvemetal anode in electrical and mechanical connection according to thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In this invention as shown inthe accompanying drawing there is provided a metal anode 1 whichaccording to the art can be either a sheet (solid or with 'variousconfigurations of openings) or an expanded mesh made from a valve metal.A metal cathode 6 of a ferrous metal, preferably iron, is provided tomake the second electrode for the bipolar cell. As with the anode 1, thecathode 6 can be either a sheet (solid or with various configurations ofopenings) or an expanded mesh. For convenience the cell separatorbetween and parallel to anode 1 and cathode 6 has not been shown in thedrawing since the present invention is not concerned with any particularcell, the use of cell separators are well known and greater clarity ofdetails of the present invention is obtained by its omission.

To one of the electrodes there must be attached, typically by welding,etc., a boss having thread engaging means for receiving and engagingbolt 5. In view of the thinness of the typical electrode, it isdesirable that each electrode be equipped with a boss which when theanode 1 and cathode 6 are properly aligned, the two bosses will mate.

with each other and properly space the electrodes at the desireddistance from the anolyte and catholyte compartment separators. Thefemale bolt receiving boss can be attached to either electrode.

As shown in the drawing the anode boss 2 is the female bolt receivingboss. Boss 2 has threads or thread engaging means which has been coatedor plated with a thin but continuous coating 3. The anode 1 boss 2 ismade of a metal which is substantially the same as the anode, that isthe boss 2 is also made of a valve metal. The coating 3 is a platinummetal which has been applied according to usual methods for platinizingobjects. One convenient method is to brush on an application of athermally reducing platinizing solution which can then be reduced to anadherent deposit by using a small hand torch. As illustrated the otherboss is the cathode boss 7 which is made of a metal substantially thesame as that of the cathode 6, namely a ferrous metal.

Again boss 7 is attached by welding or other suitable means. Boss 7contains an aperture or hole in axial alignment with a correspondinghole in cathode 6 through which bolt 5 is inserted preliminary to makingthe electrical/mechanical connection of this invention.

The bolt 5 has the usual head with pressure receiving shoulder, shankand threads at the other end. For this invention the threads are coatedor plated with a metal 4 to complete the present invention. The bolt ismade of a metal similar to the electrode through which it is inserted.As shown in the drawing the bolt is inserted through the cathode 6 andcathode boss 7, therefore the bolt 5 is made of a ferrous metal and theplating 4 is a coinage metal. For the purpose of this invention the bolt5 head may be slotted for moving the bolt 5 with a blade instrument asshown or prepared to use an Allen wrench or some other key typeinstrument. The bolt head pressure shoulders have been shown as conicalbut other configurations such as a flat shoulder can be used dependingon the thickness of the electrode and if each electrode has acorresponding boss. It will, of course, be immediately recognized thatwhen the bolt 5 is fully connected with the female boss the shoulder ofthe bolt 5 head must be engagingly seated against the electrode and/orboss so that the electrode (cathode 6 as shown) is held securely.

As the bolt 5 is engaged in the female boss 2 the bolt thread coating 4and boss thread coating 3 yield just enough to allow passage of bolt 5yet make a tight solid electrical connection and mechanical connectionunder stress. Thus, the loss of electrical energy due to resistance ofthe joint is reduced to negligible. The tightness of the joint alsoinsures a firm unyielding mechanical connection.

It follows from the foregoing that the anode boss 2 must be mated withthe cathode 6 (or cathode boss 7 if so provided) to insure that the bolthead does in fact exert pressure on and retain the cathode in place.

Those familiar with this type of art will readily recognize from theforegoing description that the benefits of this invention will beobtained regardless of whether the bolt passes through and joins to theanode 1 and its boss 2 or the cathode 6 and its boss 7. In all cases thebolt is made of metal like the electrode through which it passes. Ineach case the ferrous metal threads or engaging means are coated orplated with a coinage metal. In each case the valve metal threads orengaging means are coated or plated with a platinum metal.

In describing this invention the phrase valve metal has been used todescribe a class of metals well known in the electrochemical art. Forconvenience it sufiices to say that by valve metals it is meant themetals of titanium, zirconium, tungsten, tantulum and niobium.Preferably titanium or tantulum is employed and it is normally acommercially pure grade such as electrolytic grade. Alloys of titaniummay be employed as long as the alloy meets the criterion of passivity,metal alloys which become passivated when polarized anodically canremain passive well beyond the anodic potential needed to convert achloride ion to chlorine. The phenomenon of passivity in this connectionis discussed in an article by Greene appearing in the April 1962 issueof Corrosion, pages 136-t to l42-t wherein reference may be made to FIG.1 of the article which describes typical active-passive transition of ametal towards a corrosive medium. Titanium alloys of aluminum,vanadium,, palladium, chromium or tin can be employed in which thelatter metals are present as less than 10 percent of the alloy.

The plating for the ferrous metal is a coinage metal, i.e., copper,silver, gold. Because of solution conditions required in the directplating of these metals to ferrous metal, it is sometimes desirable tofirst plate with a step of metal such as nickel which has a moredesirable electroplating solution and then plate with the desiredcoinage metal. For instance, the use of nickel and the copper avoids theuse of a cyanide bath. Thus, describing such two step plating nickelcopper metal means the copper was plated over a thin layer of nickel.Other intermediate layers are similarly described. The two layer softmetal arrangement retains the advantages of the present invention whilepermitting the use of more desirable plating solutions. Such two stepsystem is to be considered within the scope of this invention.

The platinum group metals include platinum, ruthenium, osmium, rhodium,iridium and palladium and alloys of two or more of the foregoing metals.It has been convenient to refer to the group as platinum since platinumis the preferred metal in the group.

Many other modifications and ramifications will naturally suggestthemselves to those skilled in the art based on this disclosure. Theseramifications and modifications are intended to be comprehended aswithin the scope of this invention.

Having thus described the invention, what it is desired to claim andsecure by Letters Patent is:

1. In a bipolar electrolytic filter press cell for the production ofchlorine from an aqueous alkali metal chloride wherein the anode is avalve metal and the cathode is a ferrous metal said anode and saidcathode being in electrical connection by bolting one to another byinserting through one of the foregoing electrodes a bolt having threadengaging means and made of substantially the same metal as the said oneelectrode, the other electrode having female thread engaging means, theimprovement comprising the thread engaging means made of a ferrous metalbeing coated with a coinage metal plating and thread engaging means madeof a valve metal being plated with at least one platinum group metalwhereby when the electrical connection is made the softer platinum groupmetal and the coinage metal are driven into solid contact with eachother thereby making a solid electrical connection and a strongmechanical connection under shearing stress, said female thread engagingmeans being a metal boss containing female bolt engaging threads, saidboss being adhered to said other one electrode on the side facing saidelectrode.

2. In a bipolar electrolytic filter press cell for the production ofchlorine from aqueous alkali metal chloride solutions wherein the anodeis a valve metal and the cathode is a ferrous metal, said anode andcathode being in electrical connection by bolting one to the other, theimprovement which comprises making the electrical connection by adheringto said anode on the side facing said cathode a valve metal bosscontaining female bolt engag ing threads wherein said threads of saidboss have been coated with at least one metal from the platinum group ofmetals, inserting through said cathode a ferrous metal bolt for engagingsaid boss in tight electrical and rigid mechanical connection, said bolthaving a copper over nickel copper plating on the engaging threadswhereby when the electrical connection is made the softer platinum groupmetal and the nickel copper metal are driven into solid contact witheach other thereby making a solid electrical connection and a strongmechanical connection under shearing stress.

3. The electrical connection of claim 2 wherein adhered to the cathodein mating position with respect to said boss on said anode is a ferrousmetal boss through which said bolt will be inserted.

4. The electrical connection of claim 2 wherein the platinum group metalis platinum.

5. The electrical connection of claim 2 wherein the ferrous metal of thecathode is steel.

6. The electrical connection of claim 2 wherein the valve metal of theanode and anode boss is titanium.

References Cited UNITED STATES PATENTS 3,441,495 4/1969 Colman 2042683,271,289 9/1966 Messner 204-286 1,365,875 1/ 1921 Ward 204256 3,242,0653/1966 DeNor-a et al. 204-256 3,511,766 5/1970 Kisner et al. 204286FOREIGN PATENTS 1,054,430 4/1959 West Germany 204256 TA-HSUNG TUNG,Primary Examiner W. I. SOLOMON, Assistant Examiner US. Cl. X.R.

. $273 3? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo. 3,788,966 Dated January 9: 97

Inventor(s) Orlando W. Ste ghenson III and John E. Schmidt It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

f" Column I, Claim 1, line 17, after the word "other", 1

' please delete one".

Column l, Claim 1, line 18, after the Ward "said", please insert--one--.

In the Drawing, patentee 's first initial in his name should be changedfrom "C" to --O---.

Signed and sealed this 11th day of June 1971;.

(SEAL) Atteat:

C. MARSHALL DANN Commissioner of Patents EDWARD M.FLE1CHER.,JR.Attesting Officer

